No abstract

The hepatic stellate cell (HSC) is the primary cell type in the liver responsible for excess collagen deposition during fibrosis. Following a fibrogenic stimulus the cell changes from a quiescent vitamin A-storing cell to an activated cell type associated with increased extracellular matrix synthesis and increased cell proliferation. The phosphatidylinositol 3-kinase (PI3K) signaling pathway has been shown to regulate several aspects of HSC activation in vitro, including collagen synthesis and cell proliferation. Using a targeted approach to inhibit PI3K signaling specifically in HSCs, we investigated the role of PI3K in HSCs using a rodent model of hepatic fibrosis. An adenovirus expressing a dominant negative form of PI3K under control of the smooth muscle ␣-actin (␣SMA) promoter was generated (AdSMAdnPI3K). Transducing HSCs with Ad-SMAdnPI3K resulted in decreased proliferation, migration, collagen expression, and several additional profibrogenic genes, while also promoting cell death. Inhibition of PI3K signaling was also associated with reduced activation of Akt, p70 S6 kinase, and extracellular regulated kinase signaling as well as reduced cyclin D1 expression. Administering Ad-SMAdnPI3K to mice following bile duct ligation resulted in reduced HSC activation and decreased extracellular matrix deposition, including collagen expression. A reduction in profibrogenic mediators, including transforming growth factor beta, tissue inhibitor of metalloproteinase 1, and connective tissue growth factor was also noted. However, liver damage, assessed by alanine aminotransferase levels, was not reduced. Conclusion: Inhibition of PI3K signaling in HSCs during active fibrogenesis inhibits extracellular matrix deposition, including synthesis of type I collagen, and reduces expression of profibrogenic factors. These data suggest that targeting PI3K signaling in HSCs may represent an effective therapeutic target for hepatic fibrosis. (HEPATOLOGY 2009;50:1512-1523

Emerging evidence suggests a strong interaction between the gut microbiota and health and disease. The interactions of the gut microbiota and the liver have only recently been investigated in detail. Receiving approximately 70% of its blood supply from the intestinal venous outflow, the liver represents the first line of defense against gut-derived antigens and is equipped with a broad array of immune cells (i.e., macrophages, lymphocytes, natural killer cells, and dendritic cells) to accomplish this function. In the setting of tissue injury, whereby the liver is otherwise damaged (e.g., viral infection, toxin exposure, ischemic tissue damage, etc.), these same immune cell populations and their interactions with the infiltrating gut bacteria likely contribute to and promote these pathologies. The following paper will highlight recent studies investigating the relationship between the gut microbiota, liver biology, and pathobiology. Defining these connections will likely provide new targets for therapy or prevention of a wide variety of acute and chronic liver pathologies.

Sustained hepatic inflammation induced by various causes can lead to liver fibrosis. Transcription factor NF-κB is important in regulating inflammatory responses, especially in macrophages. We presently investigated whether an NF-κB decoy, a synthetic oligodeoxynucleotide (ODN) imitating the NF-κB binding site, inhibited the inflammatory response after CCl4 intoxication to prevent CCl4-induced hepatic injury and fibrosis. The NF-κB decoy was introduced into livers by injecting the spleens of mice, using a hemagglutinating virus of Japan (HVJ)-liposome method. ODN was transferred mainly to macrophages in normal or fibrotic livers. Increases in serum transaminases and production of inflammatory cytokines after a single challenge with CCl4 were inhibited by the NF-κB decoy, which suppressed nuclear translocation of NF-κB in liver macrophages. Liver fibrosis induced by CCl4 administration for 8 wk was suppressed by the NF-κB decoy, accompanied by diminished mRNA expression for transforming growth factor (TGF)-β, procollagen type 1 α1, and α-smooth muscle actin (SMA). In vitro, isolated liver macrophages showed increased DNA binding activity of NF-κB and inflammatory cytokine production after hydrogen peroxide treatment; both increases were inhibited significantly by the NF-κB decoy. In contrast, NF-κB decoy transferred to isolated hepatic stellate cells (HSC) had no effect on their morphological activation or α-SMA expression, although the decoy accelerated tumor necrosis factor (TNF)-α-induced apoptosis in activated HSC. The effect of NF-κB decoy suppressing fibrosis probably results mainly from anti-inflammatory effects on liver macrophages, with a possible minor contribution from its direct proapoptotic effect on activated HSC.

Endotoxin syndrome is a systemic inflammatory response mediated by inflammatory cytokines. Nuclear factor B (NF-B) is the dominant regulator of the production of these cytokines by inflammatory cells. The aim of this study was to assess the efficacy of in vivo transfer of synthetic double-stranded oligodeoxynucleotides (ODN) with high affinity against NF-B (NF-B/decoy/ODN) as a therapeutic strategy for treating endotoxin-induced fatal liver injury. Liver injury was induced by administration of lipopolysaccharide (LPS) to Propionibacterium acnes-primed BALB/C mice. NF-B/decoy/ODN was transferred into the portal vein using a fusigenic liposome with hemagglutinating virus of Japan. NF-B/decoy/ODN was preferentially transferred to Kupffer cells, and activation of NF-B after the LPS challenge was suppressed, leading to decreased inflammatory cytokine production. As a result, the massive necrosis and hepatocyte apoptosis observed in the control mice was dramatically attenuated and the survival rate improved. In conclusion, NF-B/decoy/ ODN transfer in vivo effectively suppressed endotoxin-induced fatal liver injury in mice. (HEPATOLOGY 2003;38:335-344.)